This invention relates generally to retractable tape measurement devices. More particularly, the present invention is directed to a tape measure employing power operated tape extension that may be disengaged for retraction of the tape back into a housing of the tape measure.
Retractable tape measurement devices, or “tape measures”, are well known. These tape measures generally have a housing formed by opposed sidewalls. An aperture in the housing allows an elongated tape or “blade” having measurement indicia thereon to extend out of and retract into the housing as needed. The tape is typically wound on a reel in a coil rolled manner with the reel being rotatably mounted within the housing. A first end of the tape may be attached to the reel and second free end of the tape typically has a stop or hook to prevent the second end of the tape from entering the housing. A retracting means, such as a recoil spring, is coupled with the reel to bias the reel in a direction to wind the tape onto the reel and retract the tape into the housing. A user can pull on the hook against the force of the retracting means to extend the tape out of the housing for making a measurement. A brake lever or the like may be provided so that the tape may be frictionally held at a selected position of extension while a measurement is made, and then released for retraction.
As an improvement to the operation of a conventional tape measure, power operated tape measures have been devised. The most popular design for a power operated tape measure is to include a motor that employs power operated tape extension out of the housing. This is accomplished through a gear and roller system coupled with the motor and engaging with a bottom or outwardly exposed surface of the tape as it is wound on the reel. The motor may then drive the unwinding of the tape from the reel through the gear/roller system so that the tape extends out of the housing a selected amount. Although a tape measure configured with power operated tape retraction may be implemented, such a design is often undesirable due to the complexity of employing a motor that rotates under electrical power in opposed directions to accomplish tape extension and retraction. A typical power operated tape measure, therefore, relies on a conventional recoil spring for tape retraction while utilizing a motor means for tape extension.
One design issue with tape measures having only power operated tape extension is that the gearing/rollers coupled with the motor must be disengaged from the tape surface in order for the recoil spring to accomplish quick tape retraction, i.e., without having to overcome the braking force provided by the resistance of the motor to being rotated backwardly. Various mechanisms have been employed to move a drive roller out of engagement with the tape, such as by the switch actuator and rod arrangement disclosed in U.S. Pat. No. RE37,824. However, such an arrangement is disadvantageous because as the diameter of the coiled tape becomes smaller (due to extension of a portion of the tape out of the housing), the tape driving roller must move inwardly towards the centerpoint of the reel to maintain contact with the remaining tape. This motion of the driving roller displaces the rod and actuator coupled therewith with respect to the housing, which is undesirable because the actuator does not remain in a consistent position on the housing for initiating tape retraction.